Robust Continuous Control Set Model Predictive Control in Synchronous Reference Frame for Grid-Tied Inverters

Abstract

This article proposes a continuous control set model predictive control (CCS-MPC) for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -based grid-tied inverters. The proposed controller has inherent robustness against <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> resonance and does not need an active damping loop. The controller is designed in the synchronous reference frame where the variables are dc quantified. Otherwise, it can generate a steady-state offset in the stationary frame. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> model, which is needed for the CCS-MPC design, shows a strong cross-coupling between the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> axes, and the order of the model is high. To deal with the cross-coupling, a multi-input multioutput CCS-MPC is designed, and to reduce the order, system identification is used to build the process model. The optimization of CCS-MPC is performed offline, and a low real-time computation is needed. Moreover, the controller’s output is applied by a modulator, and it operates with a fixed switching frequency. To guarantee the closed-loop stability, the controller parameters are selected by a sensitivity analysis. The simulation and experimental results are presented to validate the proposed controller’s appealing features.